Thread (69 messages) flat view 69 messages, 5 authors, 2020-10-16

Re: [PATCH v3 03/10] bloom: fix logic in get_bloom_filter()

From: SZEDER Gábor <hidden>
Date: 2020-06-27 16:33:42

On Fri, Jun 26, 2020 at 12:30:29PM +0000, Derrick Stolee via GitGitGadget wrote:
quoted hunk ↗ jump to hunk
From: Derrick Stolee <redacted>

The get_bloom_filter() method is a bit complicated in some parts where
it does not need to be. In particular, it needs to return a NULL filter
only when compute_if_not_present is zero AND the filter data cannot be
loaded from a commit-graph file. This currently happens by accident
because the commit-graph does not load changed-path Bloom filters from
an existing commit-graph when writing a new one. This will change in a
later patch.

Also clean up some style issues while we are here.

Helped-by: René Scharfe [off-list ref]
Signed-off-by: Derrick Stolee <redacted>
---
 bloom.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/bloom.c b/bloom.c
index c38d1cff0c..2af5389795 100644
--- a/bloom.c
+++ b/bloom.c
@@ -186,7 +186,7 @@ struct bloom_filter *get_bloom_filter(struct repository *r,
 	struct diff_options diffopt;
 	int max_changes = 512;
 
-	if (bloom_filters.slab_size == 0)
+	if (!bloom_filters.slab_size)
 		return NULL;

 	filter = bloom_filter_slab_at(&bloom_filters, c);
@@ -194,16 +194,14 @@ struct bloom_filter *get_bloom_filter(struct repository *r,
 	if (!filter->data) {
 		load_commit_graph_info(r, c);
 		if (c->graph_pos != COMMIT_NOT_FROM_GRAPH &&
-			r->objects->commit_graph->chunk_bloom_indexes) {
-			if (load_bloom_filter_from_graph(r->objects->commit_graph, filter, c))
-				return filter;
-			else
-				return NULL;
-		}
+		    r->objects->commit_graph->chunk_bloom_indexes)
+			load_bloom_filter_from_graph(r->objects->commit_graph, filter, c);
 	}
 
-	if (filter->data || !compute_if_not_present)
+	if (filter->data)
 		return filter;
+	if (!compute_if_not_present)
+		return NULL;
Some callers of get_bloom_filter() invoke it with
compute_if_not_present=0, but are not prepared to handle a NULL return
value and dereference it right away:

  write_graph_chunk_bloom_indexes():

                struct bloom_filter *filter = get_bloom_filter(ctx->r, *list, 0);
                cur_pos += filter->len;

  write_graph_chunk_bloom_data():

                struct bloom_filter *filter = get_bloom_filter(ctx->r, *list, 0);
                display_progress(progress, ++i);
                hashwrite(f, filter->data, filter->len * sizeof(unsigned char));

I don't know whether this was an issue before, but I didn't really
tried.  Unfortunately, starting with this patch this causes
segmentation faults basically in all real repositories I use for
testing.

  expecting success of 9999.1 'test': 
          for i in $(test_seq 1 513)
          do
                  >file-$i || return 1
          done &&
          git add file-* &&
          git commit -q -m one &&
  
          git commit-graph write --reachable --changed-paths
  
  Segmentation fault
  not ok 1 - test


  Program received signal SIGSEGV, Segmentation fault.
  0x0000000000515848 in write_graph_chunk_bloom_indexes (f=0x9fe650, 
      ctx=0x9d2000) at commit-graph.c:1101
  1101                    cur_pos += filter->len;
  (gdb) print filter
  $1 = (struct bloom_filter *) 0x0


 	repo_diff_setup(r, &diffopt);
 	diffopt.flags.recursive = 1;
-- 
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